1. Field of the Invention
The invention relates to a vehicle height adjustment device, and more particularly, to an improvement in the control of recovering the operation of the vehicle height adjustment device.
2. Description of the Related Art
Conventionally, a vehicle height adjustment device changes the vehicle the vehicle height by controlling the supply and discharge of the fluid in accordance with the condition of vehicle being used and the running state of the vehicle. For example, the vehicle height may be reduced to facilitate the entry and exit of a passenger from the vehicle. The vehicle height may also be adjusted such that the height of a platform coincides with the height of a luggage carrier to facilitate the loading and unloading of a piece of luggage from the vehicle.
A vehicle height adjustment device described in Japanese Patent Application Publication No. 11-198625 (JP-A-11-198625) automatically adjusts the vehicle height to a target vehicle height. In particular, a suspension control means is disclosed that suspends the supply of a fluid for a predetermined time to protect a fluid system, which includes fluid pumps, hydraulic cylinders, and the like, when the target vehicle height cannot be achieved due to excessive load or when the fluid system is overloaded although the target vehicle height is achieved.
The vehicle height at a particular wheel may decrease if the vehicle runs on a rock while running on a bad road or runs on a curbstone even while running normally. In this case, the internal pressure of the hydraulic cylinder that controls the vehicle height at the particular wheel rises and may exceed the aforementioned protection pressure even though the actual vehicle height is not raised, whereby the execution of the vehicle height control may be temporarily suspended. Once the failsafe of the suspension, takes place, the failsafe cannot be canceled simply. In general, the failsafe cannot be canceled without going through a predetermined cancellation step.
Once the particular wheel leaves bad road running section or gets off the curbstone, the vehicle height should be increased. However, due to the aforementioned failsafe, the internal pressure of the hydraulic cylinder is high, so that the control of temporarily suspension remains. Therefore, the vehicle height cannot be swiftly raised in an attempt to reach an appropriate vehicle height. As a result, the vehicle is inclined and causes a sense of incongruity to passengers therein.